Virginia Trimble to Speak on "The Universe You Don't See: Existence and Nature of Dark Matter"

NOV 2 2 1994

National Capital Astronomers, Inc. 3011320-3621

Volume 53, Number 4 December, 1994 ISSN 0898-7548

by Harold Williams

The next meeting of the National Capi- Matter Problem." The 5th Annual As- The mathematics needed to understand tal Astronomers will be held on Satur- trophysics Conference in Maryland Oc- this in detail are only what is required in day, December 3rd, at 7:30P.M., in the tober to through 12 at College Park was the first part of any physics class. How Bunim room on the ninth floor of the devoted to this topic this year. There is many scientific fields can you be put on Clinical Center (Building to) at the much diverse evidence leading to the the frontier when you take the first intro- National Institutes of Health (NIH). conclusion that most of the universe is ductory course? I think very few. Virginia Trimble of the University of dark. The most convincing evidence is Maryland will speak on "The Universe the flat rotation curves of disk galaxies. The mathematics follows. For those You Don't See: Existence and Nature of The argument goes as follows-stars in who this does not make physical and Dark Matter." The speaker sent the disk galaxies move in predominately algebraic sense you may skip to the end following abstract: "Many different circular orbits. Newton's Laws and of the article where the speaker is de- lines of observational evidence indicate Newtonian Universal Gravity tell us scribed. strongly that 90% or more of the gravi- that the mass enclosed in a spherical or tational potential of the universe comes cylindrical symmetric is determined by Newton's Universal Law of Gravity: from matter which does not emit its fair the velocity ofthe orbiting bodies. The share of light or other electromagnetic mass, as measured in light and the veloc- F=GMm radiation. This is the infamous dark ity of stars, do not agree. The mass in R2 matter, and its existence has been firmly stars in the center of most galaxies de- where 1':is the force, G is the Newtonian established for nearly 20 years. But we creases as a power law to the minus 3.4 gravitational constant,Mis one mass, m know remarkably little about what it is. power. The mass, in stars in the disk of is the other mass (the one whose accel- Candidates range from neutrinos with most galaxies decreases exponentially. eration we will consider), and R is the rest masses of a few eV through other, The mass as measured by its doppler distance between M and m. even stranger particles, to substellar shifted light of the stars whirling around objects and 106 solar mass black holes. the galaxy, in fact, not only does not Since gravity is a central force, it acts A range of laboratory experiments and decrease like the mass in luminous stars, only on the mass internal to radius R, if astronomical searches, currently in but it increases linearly with the distance the mass distribution is symmetric in R. progress, could identify the most likely away from the galaxy. The dark matter Since disk galaxies are symmetric inR, candidate(s) in the near future, but could phenomenon is indeed this glaring error we can write the force on a star of mass also leave the issue unresolved indefi- between these two different techniques mas: nitely." for measuring mass, by it luminous ef- F=GM(R)m fect and by its gravitational potential, as R2 The largest unsolved problem in all of evidenced by the motions of the stars astronomy and physics is the "Dark that we see doppler shifted. See Trimble, Page 3 :I: VeCem6e~Calendar

The Public is Welcome!

Friday, December 2, 9, and 30,1994,8:30 PM-Open Washington-Baltimore region. Information: USNO nights with NCA's Celestron 14-inch (0.36 meter) Public Affairs Office, 202/653-1541. telescope at Ridgeview Observatory, 6007 Ridgeview Drive (off Franconia Road between Telegraph Road Tuesdays, December 6,13,20, and 27,1994,7:30 andRoseHill Drive). Information: Bob Bolster at 703/ PM-Telescope making classes at Chevy Chase Com- munity Center, Connecticut Avenue and McKinley 960-9126. Street, NW. Information: Jerry Schnall, 202/362- Fridays, December 2, 9,16,23, and 30,1994,7:30 8872. PM-Telescope making classes at American Univer- sity, McKinley Hall Basement. Information: Jerry Wednesday, December 7, 1994-December "Sky Watch" column by Blaine P. Friedlander, Jr. appears Schnall, 202/362-8872. in The Washington Post "Style" section. It lists many Saturday, December 3, 1994, 7:30 PM-The Decem- other events for the month. berNCA meeting will feature Virginia Trimble speak- Saturday, December 17, 19947:30 PM-"Exploring ing about "The Universe You Don't See: Existence the Sky" telescope viewing at the open field in Rock and Nature of Dark Matter." Creek Park nearest to the Nature Center. NCA mem- Saturday, December 3,1994,5:30 PM-Dinner with bers please bring telescopes. For more information, the speaker at the La Posada Restaurant, 8117 call John Lohman, 703/820-4194 Woodmont Ave., Bethesda, MD., before the monthly Saturday, December 24, 1994, Night-December's meeting. Reservations are for 5:30 p.m., sharp. second best night for dark-sky observing and "absorb- Saturday December 3, 1994, Night (After The ing" ("Moon-dark" until around Midnight). See De- Meeting)-December's best Saturday night for dark- cember 3rd listing. sky observing, and "absorbing" (Moon sets by 8:15 Saturday, December 31, 1994, Night-December's p.m., providing nine hours of "Deep Night," weather third best night for dark-sky observing and "absorb- permitting, until dawn, Sunday morning). Several ing" ("Moon-dark" until around Midnight). See De- relatively light-pollution-free sites are available for cember 3rd listing. NCA members's use. Information: Daniel Costanzo, 703/841-4765. Friday, January 6, 1995, 7:00-8:30-Sandy Spring Friends School Presents, Star Party: Astronomy Ac- Mondays, December 5, 12, 19, and 26, 1994, 8:30 tivities. Free to the public. See the ad on page 5. PM-Public nights atU.S. Naval Observatory (USNO), in Northwest Washington, DC (off Massachusetts Saturday, January 7, 1995,7:30 PM-The January Avenue). Includes orientation program on USNO's NCA meeting will feature Dimitris Christodolou mission, viewing of operating atomic clocks, and speaking about "The Formation of Binary Stars glimpses through the finest optical telescopes in the through Fission of a Single Mass: Past and Present."

Mark Your Calendar! - Next Six NCA Meetings

Below are dates for the next six NCA meetings coming up after this December's meeting unless otherwise indicated. January 7 April 1 February 4 May 6 March 4 June 3

Page 2 TRIMBLE, from page I whereM(R) is the mass enclosed within remembering that an isothermal fellow of many learned societies and a radius R. sphere-uniform temperature sphere serves on advisory panels and commit- where the temperature causes pressure tees too numerous to mention. Her ser- Newton's second law of motion: which is balanced by the inward force of vice as an article reviewer, writer of gravity has a mass distribution propor- reviews, editor, and speaker are legion. F=ma. tional to r". What the creator is trying to She is currently the associate editor of The geometry of acceleration in a circle: tell us here has not been fully fathomed theAstrophysicalJoumal. Her publica- by anyone yet. tions are also legion. Her resume is so a(R) = x(R)2 well organized that I have never seen a R Our speaker, Virginia Trimble, is both better one. I am going to modify my Combining the equations: bicoastal and biacademic and is profes- resume along the lines of hers as soon as sor at the University of Maryland at I get time. Once you have heard her m L= GM(R)Y1l! College Park and the University of Cali- speak, you wiII go out of your way to R R2 fornia at Irvine. She is a member and hear her speak again. Solving for the velocity of a star m at radius R yields:

x(R) =VG~(R)

Keplerian motion results when all of the I '-' 200 mass is concentrated in the center so 1 x(R)=~ '3 ~ 100 This would make the velocity fall off proportional to ViTR.

The velocity of the planets around the o 20,000 40,000 60,000 sun and the velocity of the moons Distance from center of galaxy (ly) around a planet follow Keplerian rotation to fairly -0gh order falling off pro- The rotation curves of stars within our own galaxy. (Kaufmann: UNIVERSE, Third portional to / R . Edition © 1991, W H. Freeman and Company)

BUT Disk Galaxy rotation is FLAT. To first order it does not vary with radial distance except in the very center of the 350 galaxy. There is a huge difference between decreasing proportional to ~ 300 NGC4378 and remaining constant or nearly flat. ---- 250 One can go one step further and invert ~ NGC 1620 "0 200 , NGC7664 the equation, solving for the mass within 0 a radius R and one finds 8. '" \ , ] 150 -, R :e -,, MIRJ =J;

Page 3 The f3 Pictoris Phenomenon in Herbig AelBe and A-shell Stars

Reviewed by Harold Williams

On Saturday November 5, 1994 at its high Earth orbit, objects in the sky with the regions where lithium the National Institutes of Health are not constantly occulted by the would be destroyed by fusion in the (NIH), Carol Ann Grady of the Ap- Earth. core. Because of this fact A stars do plied Research Corporation spoke to not have a lithium abundance clocks us on "The f3 Pictoris Phenomenon The Infrared Astronomical Satellite like G stars do. in Herbig Ae/Be and A-shell Stars." (lRAS), discovered circumstellar Carol got her B.S. from Washington dust disks around several stars like f3 For a star to be a Herbig Ae/Be star University in Saint Louis and her Pictoris and a Lyrae-Vega. Vega, it must have emissions in at least one Ph.D. from the University of Colo- in fact, is a primary spectrophoto- of the Balmer series transitions. rado, where Ted Snow was her dis- metric standard star and its infrared Since the dust has an excess in the sertation advisor. Her Ph.D. disser- excess emission from the dust disk infrared, one might ask why we look tation was titled, "Stellar Winds in causes some problems in its use as a in the UV. The reason why the UV Classical Be Stars." Carol has held primary spectrophotometric stan- is so interesting is because at those a number of NASA support posi- dard. These dust disks cannot be fit wavelengths, it is easier to look at the tions when she worked for the Com- with a single temperature spatially gas. Also, there are transitions in the puter Sciences Corporation (before extended disk, but with a spatially UV for Fe, Mg, Mn, Cr, Ti, Zn, Si, C, Hubble Space Telescope was extended multitemperature disk. and N. In fact, at IUE UV wave- launched) as a systems analyst dur- The light in the ultraviolet (UV) ob- lengths one can see Sill, SiIlI, and ing calibration. Instead of serving in tained from the IUE shows silicate SiIV. Silicon is one of the main a NASA support position to assist features from dust less than one mi- ingredients of a terrestrial planet. Of other scientists, she now holds a cron. In fact, some of the spectral the 62 stars observed, 32 have been NASA long-term space astrophys- features look like Halley's comet. f3 observed with high spectral resolu- ics five year grant to do her own Pictoris has dust which is warmer tion so that motion caused by research. So instead of supporting than most A-shell stars. At least one doppler shifts in spectral lines can be NASA she is supported by NASA. third of nearby A stars show dust detected as small as 25 krnls. When Carol is principal investigator or disks like Vega, Formalhault, and E these stars are observed, they show lead PIon several projects. She Eridani. that gas is being accreted into these coordinates observations with the pre-main-sequence stars because International Ultraviolet Explorer One of the questions that can be material is observed spectroscopi- (IUE), which was launched in 1978 asked is how typical is f3 Pictoris cally to be falling into the star. and is controlled from the Goddard and, in fact, how old is the star? Sometimes the dust clouds, as they Space Flight Center. This satellite is Stars with spectral class A are very orbit the central star, will occult the still going strong and is one of the hot compared to G stars like our Sun. star and allow us to get spectra of the most successful space-based tele- The Sun has a large convective zone stars atmosphere as if you had a scopes of all times. She is mining the so it has a lithium abundance clock. stellar coronagraph like the solar IUE digital archived data as well as But A stars being much hotter have corona~raph machines. taking new IUE data. This space- very small convective zones only craft has control in real time. Due to near the surface so no mixing occurs As usual, we are indebted to NIH and NCA member Jay Miller for arrang- Montgomery; College's Public Planetarium ing to meet at NIH, where he works, and to use the Bunim room on the ninth floor. It was even a little fun Exciting public planetarium programs are offered at Takoma Park's own planetarium. Astronomy is one of the few sciences accessible to any inquiring mind. see Jay perplexed at himself when he realized that he had left the keys to All programs begin at 7:00 p.m. There is no admission charge. the room and his identification as an Thursday, December 22, 1994 NIH person at home or in his NIH office in another building, and he "The Day of the Sun's Return" had to charm the guard into letting us in. Fortunately Jay's charm pre- The planetarium is located on Fenton Street on the Takoma Park campus of vailed rather rapidly. For those of us Montgomery College. It is attached to the Science South building on the ground who sometimes forget things, it was level and has a conspicuous silver-colored domed roof. nice to see that Jay, too, is human.

Page 4 Occultation and Grazing Updates midway between 42 and 43 Ceti; the 12000 coordinates of SAO 129245 are by R.A. Ih 21m 13.8s, Dec. -1 deg.06' David Dunham 52"; the B1950 position is R.A. Ih 18m 40.6s, Dec.-l deg. 22' 33". Although the November 18th occultation is 1.04" north (18.6 path widths), tion event has passed, we decided to probably +/-0.2" (3.6 path widths) and Both objects were on the CCD expo- include it in this newsletter to give the time correction is +4.5 minutes +/ sures, so the results, although reduced members who are inexperienced with -0.6 minute. The closest approach with Guide Star Catalog (GSC) data, occultations a flavor for the activity. time should be 5 :08 UT in Newfound- should be fairly accurate. The formal Unfortunately, weather precluded land, 5: lOUT in the northeastern uncertainty in the path is 0.09", 1.5 good observations of this event. We USA, 5:13 UT at Winnipeg, 5:15 UT times Eichsfeldia's angular diameter hope that this edition is delivered to all in Alberta, and 5: 17 UT in the of 0.06" (linear diameter expected to interested members before the No- Vancouver, BC area. be 67 km), but due to a relatively poor vember 26th occultation event in distribution of the reference stars, Maryland. - Eds. Please alert others in your area to the Pravec thinks that the error is about possibility of this event so that we can 0.2", just over three path widths +/-. On November 16th, Petr Pravec, get better coverage of the occultation, There is some chance that Pravec can Ondrejov Observatory, obtained 5 and practice finding the target star. If get more measurements shortly after CCD images of 442 Eichsfeldia, oc- an occultation occurs, the magnitude sunset Thursday at Ondrejov, when cult the 9.0-mag. star SAO 129245 on drop should be about 5 and the ex- the objects will be close enough to November 18 at 5h U.T. (Thursday, pected central duration is 10.6 sec- eliminate the poor distribution prob- night). The observations show a onds. The event will occur at rather lem of the Nov. 16th observations. strong northward shift of the path, high altitude for all potential observ- That could allow a very accurate pre- crossing central Canada from east to ers, with no twilight interference, but diction. Such an update might be west, but passing a little south in the the full Moon will be 37 deg. away. available as early as 21h UTNov. 17, western part, so that Edmonton, No finder chart has been published for and if so, Iwill distribute it bye-mail. Alberta, has a reasonable chance for this event in Sky and Telescope, and it The status can be found by telephon- an occultation. I think the uncertain- is also not in the main 1994 Asteroidal ing the IOTA occultation line at 301- ties are large enough that observers Occultation Supplement to Occulta- 474-4945. throughout southwestern Canada are tion Newsletter distributed to O.N. encouraged to monitor the star for a subscribers over a year ago. A finder Detailed path information will be sent possible occultation, and observers in chart is in the extra supplement, if you in a separate message to Douglas the northern U.S.A. may also want to requested and obtained that from the Hube in Edmonton, and will be sup- watch from pairs of stations for pos- McManuses in Topeka. If you don't plied to others upon request. On Nov. sible secondary occultations by pos- have this chart, you can locate the star 26 at about 3:15 UT (Friday evening sible satellites of the asteroid. The on Uranometria 2000 or Atlas Nov. 25 local time in North America), correction to my nominal path predic- Eclipticalis in northern Cetus several tenths of a degree south of a point See UPDATES, on page 6 Though this image is shown in black and white, the original color image is madefrom images taken by the imaging system on the Galileo spacecraft about 14 minutes before its closest approach to asteroid 243 Ida on August 28, 1993. This picture is madefrom images through the 4100- angstrom (violet), 7560 A (infrared), and 9600 A (infrared) filters. The camera is sensitive to near-infrared wavelengths of light beyond human vision. Shadings in the image indicate changes in illumination angle on the many steep slopes of this irregular body as well as subtle color variations due to differences in the physical state and compostion of the soil (regolith).

PageS UPDATES,Jrom Page 5

the lto-km asteroid 514 Armida will occult the 10.6-mag. star PPM 117739. Preliminary astrometry by Pravec indicates a path crossing Swit- zerland, central France, southern Georgia, and central Mexico, but the uncertainties in the GSC-based observations are large; the event could occur anywhere in the U.K., southwestern Europe, southeastern Canada, the eastern and southcentral USA, and Mexico. Attempts will be made next week to improve that prediction; if you won't have e-mail access during the Thanksgiving holiday, you might want to call the IOTA occultation line to get updates for that rather good event. Occultation Newsletter subscribers in the areas mentioned above might want to request the chart for that Important Numbers event from the McManuses in To- peka, if they don't have the EXTRA For Information supplement (again, it's not in the main one that was distributed to North Smithsonian Sky Watchers' Report American subscribers) to the North Non-technical information recording on astronomical events, objects, and American Asteroidal Occultation phenomena in the Washington, D.C. region's sky. Updated weekly. Supplement for 1994. 202/357-2000 Sky & Telescope's "Skyline" December Lunar Grazings Moderately technical information recording on latest in space technology, On December 26th, at 3:22 AM EST, astronomy, and related sciences. Updated weekly, or sooner if necessary. near Hamden, Connecticut, there will 617/497-4168 be a lunar grazing of X Virginis, a 4.8 magnitude star, at a cusp angle of 4°S, McDonald Observatory's "Star Date" when the moon is 44% sunlit. Non-technical information on space technology, astronomy, and related subjects. Broadcast weeknights, around 8:00 PM, by listener-supported public radio station WAMUFM88.5 On December 29th, at 6:42 AM EST, near Aberdeen, Maryland, there will U.S. Naval Observatory's Time Service be a lunar grazing of 40 Libra, a 5.5 Accurate Eastern Time (in 24 hour mode) and Universal Time given every few magnitude star, at a cusp angle of 2°S, seconds. Excellent for synchronizing clocks and watches. (Voice Recordings) when the moon is 13% sunlit. 202/653-1800, 900/410-TIME, and 303/499-7111; (Modem Time Service) 202/653-0351 NOAA "Space Weather" Indices Newsletter Deadline for Highly technical, but quite useful recording on Solar activity and its effect on January Star Dust Planet Earth. From the National Oceanic and Atmospheric Administration Thursday, ~ (NOAA). Updated every three hours. 303/497-3235 (anytime) or WWV at 2.5, .,0\~, 5, 10, 15, and 20 MHz (18 minutes after every hour) December 15, 1994 ':" .. : ': . Weather, Sunrise/Sunset, & UV Index Send Submissions to Gary & Alisa Recording of latest weather forecast out to five days, plus Sunrise/Sunset times, ~Qaquin, at 7821 Winona. Ct., and forecasted Solar ultraviolet radiation index. Covers Washington, DC and Annandale, VA, 22003, or send an vicinity. 703/260-0307 ASCII file viaE-Mail at 71561.1747 NCA Artificial Satellite Prediction Service @compuserve.com or fax to 7031 Customized prediction of viewing opportunities. These objects are frequently 658-2233. Submissions must be on clearly visible with unaided eyes or binoculars, even from light polluted areas. time or they may not get in. Iiappy Contact Walter I. Nissen, Jr., (voice phone) 216/243-4980, (modem) Holidays. . [email protected]

Page 6 National Capital Astronomers, Inc.

SERVING SCIENCE & SOCIETY SINCE 1937 Consumer Workshops on selection, use, and care of binoculars NCA is a non-profit, membership supported, volunteer run, public- and telescopes, provide myth-breaking information, guid- service corporation dedicated to advancing space technology, as- ance, and demonstrations for those contemplating acquiring tronomy, and related sciences through information, participation, their first astronomical instrument. and inspiration, via research, lectures, presentations, publications, Dark-Sky Protection Efforts educate society at large about the expeditions, tours, public interpretation, and education. NCA is the serious environmental threat oflight pollution, plus seek ways astronomy affiliate of the Washington Academy of Sciences (WAS). and means of light pollution avoidance and abatement. NCA All are welcome to join NCA. For information: 3011320-3621 or is an organizational member of the International Dark-Sky 703/841-4765. Association (IDA), and the National Capital region's IDA representative. SERVICES & ACTIVITIES: Classes teach about subjects ranging from basic astronoiny to Monthly Meetings feature presentations of current work by re- hand-making a fine astronomical telescope. NCA's instruc- searchers at the horizons of their fields. All are welcome; there tors also train educators in how to better teach astronomy and is no charge. See monthly Star Dust for time and location. related subjects. NCA Volunteers serve as skilled observers frequently deploying Tours travel to dark-sky sites, observatories, laboratories, muse- to many parts of the National Capital region, and beyond, on ums, and other points of interest around the National Capital campaigns and expeditions collecting vital scientific data for region, the Nation, and the World. astronomy and related sciences. NCA volunteers serve by Discounts are available to members on many publications, prod- assisting with international scientific conferences, judge sci- ucts, and services, including Sky & Telescope magazine. ence fairs, and interpreting astronomy and related subjects Public Sky Viewing Programs are offered jointly with the during public programs. National Park Service, the Smithsonian Institution, the U.S. Discussion Groups exchange information, ideas, and questions on Naval Observatory, and others. preselected topics, moderated by an NCA member or guest NCA Juniors Program fosters children's and young adults' expert. interest in space technology, astronomy, and related sciences Publications received by members include the monthly newsletter through discounted memberships, mentorship from dedicated ofNCA, Star Dust, and an optional discount subscription to Sky members, and NCA's annual Science Fair Awards. & Telescope magazine. Fine Quality Telescopes up to 36-cm (14-inch) aperture are NCA Information Service answers a wide variety of inquiries available free for member's use. NCA also has access to about space technology, astronomy, and related subjects from several relatively light-pollution-free sites in Maryland, Vir- the public, the media, and other organizations. ginia, and West Virginia.

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Page 7 Getting to the NCA Monthly Meeting Metrorail Riders - From Medical Center Metro Stop: Walk down the hill, pass the bus stops and turn right at the anchor Exit 36 Exits 34 & 35 onto Center Drive (walking time about 10 minutes). Con- tinue uphill to Building 10, the largest building on campus. Also, the 12 bus line connects the Bethesda (7:16 PM) and NIH (7:23 PM) Metro stops with Building 10 (7:25 PM). La Posada Restaurant - Take Wisconsin Avenue toward Bethesda and bear right onto Woodmont A venue (or take the next right onto Battery Lane). Follow Woodmont to Rugby Avenue (1 blocks south of Battery) and look for the .c restaraunton your left (across from Rugby, 8117Woodmont). 1:: ~ Parking may be found on Woodmont, on Rugby, in a local (Building 10 is the tallest parking lot one block down on Rugby from Woodmont, and building on NIH campus) opposite the restaraunt entrance. Seats are not guaranteed after 5:30PM. Enter Bnilding 10 from Entrance; passing through the!!~.jble Star Dust is published ten tiriles yearly (September through doors. Go straight ahead to of Medical. Center ~ four elevators. Go to the 9th floor. The Metrorail Stop -- June) by Nationill Capital Astronomers, Inc. (NCA), a Bunim Room is just behind the glass (Red Line) partition across from the elevators. If non-profit; astronomical organization serving the entire unsure, ask for directions at the National Capital region, and bey!>nd. NCA is the as· Information Booth inside Main Entrance. tronomy affiliate ofthe Washington Academy ot Sciences (WAS) and the National Capital r· n's International Dark·Sky tion (IDA) repr A's Phone Battery Lane Nprilbers: . 3621 o~·r 0 . esident, Rugby Wayne H. , r., 30 424 . .ea for Sltll'- Map Not To Scale Dust Is the .... the preced ng month. Edi . Ailsa & Gary Joaquin, 7821 Winona Ct., Annandale, VA 22003, 7031750.1636171561.1747 @compuserve.com. .

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lllll\1\ 111\ 1111111111111 It Ill. 11111111I111l11H111 !tIl till I11 Addendum to Newsletter

GEOSTATIONARY SATELLITE GRAZES ORION NEBULA THIS MONTH

The communication satellite IS5F13 (Intelsat Series 5, No. 13) passes about one-half degree south of the trapezium in the center of the Orion Nebula each night this month at convenient times and at a near full phase. This satellite is 37,000 kilometers up in space and appears about 11th magnitude. I have seen it twice with the NCA's Celestron-14 at Bob Bolster's observatory just south of the Beltway in Alexandria. Under darker skies it probably can be seen with a telescope having an aperture as small as ten inches.

With clock drive turned off, this satellite appears stationary as the background stars drift slowly westward by it. One gets the illusion that the satellite is moving eastward, but it never leaves the field as long as the telescope is not moved.

In the Washington metropolitan area IS5F13 will pass about four arcminutes south of a fourth-magnitude double star (SAO 132298 & 132301) that is just southwest of 2.8-magnitude 44 iota Orionis. Both the double and 44 Ori are prominent near the lower edge of the cover of the December issue of Sky & Telescope magazine.

The dates and times of these passages are as follows:

Date Time EST Date Time EST Dec. 1 11:11 p.m. Dec. 23 9:45 p.m. 5 10:55 27 9:29 9 10:40 31 9:13 13 10:24 (Note: Moon interferes between 13th & 23rd.)

Notice that the satellite passes the vicinity of this double star about four minutes earlier each night. Times for intervening dates can be determined by subtracting multiples of four minutes from the times on earlier dates. I would appreciate getting observations of the timings of the passages due south of the double and estimates of its brightness then. Good luck! Leith Holloway 3011564-6061

OBSERVER'S HANDBOOK

Copies of the "Observer's Handbook" for 1995, published by the Royal Astronomical Society of Canada, will be on sale for $12 apiece at the December 3,1994 NCA monthly meeting and at all subsequent meetings until they are sold out. Please bring a check made out to "National Capital Astronomers" rather than cash. If you wish to buy a copy but cannot attend the meeting, please call me evenings or weekends to make other arrangements. Thanks.

Jeff Norman, (202) 966-0739